Traditionally, the search for better combat vehicle armor has emphasized stronger and tougher materials to resist more durable projectiles moving at higher velocities. Conventional approaches have led to progressively thicker armor, harder armor, and, inevitably, to heavier armor, and a corresponding sacrifice in vehicle mobility.
In extensive studies of armor, a surprising material feature was noticed which has given new impetus to materials armor design. Specifically, it involved the anomalous differences in ballistic behavior between aluminum armor and steel armor at low and high obliquities. People with a great deal of armor experience began to ask: why does a material having one-third the strength of armor steel sometimes show better results against projectiles than steel does?
Assuming no change in projectile form, the most apparent answer points to the thickness or path presented by the armor to the projectile. The greater the length of this path the greater the work resistance or consumption of projectile energy. The lower the density of the material, the greater the "work path" for a given weight of armor. If this feature were combined with high strength, even greater ballistic capability could be provided in a chosen material configuration. The effectiveness of this lower density core is further improved if the shape or form of the projectile is altered. This is accomplished by the hard steel front plate which can crack or fracture the projectile.
The medium strength steel back plate adds shock toughness to the total material system and facilitates easy fabrication since a weldable steel is present on both faces of the armor package. Thus, the invention presents an armor concept which attempts to accentuate the ballistic advantage of increased penetration resistance available in a low density-high strength material through a composite material arrangement.